1. Field of the Invention
The present invention is directed to devices for detecting at least one property of a fluid medium, e.g., a fluid medium flowing through a flow tube in a main flow direction. The fluid medium may basically be gases and/or liquids, in particular air, for example intake air in an intake manifold of an internal combustion engine of a motor vehicle. However, other fields of use are also conceivable. The at least one property to be determined may basically be any physical and/or chemical parameter of the fluid medium. In particular, the property may be a flow property, e.g., a flow velocity and/or a mass flow rate and/or a volume flow rate.
2. Description of the Related Art
The detection device is described with reference to an air flow rate measurement, e.g., in the intake manifold of an internal combustion engine. Numerous air flow meters are known from the related art, for example from Robert Bosch GmbH: Sensoren im Kraftfahrzeug [Sensors in the motor vehicle], edition 2007, pp 140-142. Other examples of such air flow meters are known from German patent application documents DE 10 2008 042 164 A1, DE 10 2007 024 865 A1 and DE 10 2008 042 807. In particular, these devices may be so-called hot-film air flow meters which as a rule are designed as plug-in sensors and which include at least one channel through which a portion of the flowing fluid medium is guided. For example, the plug-in sensor may be introduced into a flow tube, and a portion of the flowing fluid medium is guided through a channel of the plug-in sensor. In the channel, a sensor element, e.g., a hot-film air flow meter chip, is usually situated which includes at least one heating element and at least two temperature sensors situated upstream and downstream from the heating element. A mass flow rate of the fluid medium, e.g., of the intake air, may be inferred from an asymmetry of the temperature distribution.
In many hot-film air flow meters of the type described, the channel ends in an outlet opening. This outlet opening is in many cases formed within a removable cover of a housing of the plug-in sensor, e.g., on a side wall of the plug-in sensor and/or on a front side of the plug-in sensor. Due to the installation tolerances and/or the manufacturing tolerances, the design and/or the positioning of the cover in the area of this outlet opening may, however, change, so that the geometry of the outlet opening may be subjected to variations. Thus, overhangs of the cover over the opening may form, for example, which may result in additional eddies and a pressure drop in the area of the outlet opening. These, in turn, may influence a flow through the channel and thus have an effect on the measurement accuracy of the hot-film air flow meter. A device of the above-mentioned type would thus be desirable which is manufacturable in a simple and cost-effective manner with high precision and reduced tolerance in the area of the outlet opening.